MBP Prepare for Sale??

After much deliberation I have decided to sell my MBP in favor of returning to Windows. I have already backed up all my personal documents, files, pictures etc and deleted them from the MBP
However not being overly familiar with OSX what is the best process to prepare the system for a new owner so that none of my personal information remains on the system. Unlike a Windows based system I dont know the re-install process. Also the MBP came with Leopard and I upgraded to Snow Leopard  can Snow Leopard be reinstalled without having to install Leopard first etc etc .any help greatly appreciated.

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